I’ve noticed some users concerned or confused by the R and B gain values that they see in the cameras white balance settings after dialling in a custom white balance and tint or after taking a white balance from a white card. The R and B gain values indicate the offset that is being applied to the Red and Blue channels relative to the Green channel.
Typically the concern occurs when someone has used a white card to set their white balance and then these seemingly random numbers appear against the Red and Blue gain. But they are not random, they are expected, normal, and not normally something to every worry about.
The FX6 and FX9 are set up such that the indicated Red and Blue gains will only ever both be 0 when the white balance of the camera is at exactly 3200K. Whenever the white balance is not 3200K there will be an offset to the R and B gain. It is these offsets that balance the Red and Blue levels so that the white balance appears correct. At a lower colour temperature the will be a negative blue value and a positive red value. Above 3200K there will be a positive Red value and a negative Blue value. A positive tint value will make both the Red and Blue more positive and a negative tint value will make both the Red and Blue values more negative.
All of this is perfectly normal and perfectly expected. If you have taken a white balance off a white card and then dial in a preset value you might find that the you can’t get the last 2 digits back to a zero, so, for example after white balancing of a card you have 3653K but you then try to dial in 3200K, but the closest you can get is 3193K or 3213K. This is because the smallest steps the colour temperature changes in is 20K (on the FX6 above 5640K the steps gradually get larger and larger). But this really isn’t something to worry about 3193K or 3213K are both so close to 3200K that either will do and calibration and temperature differences will mean that the actual variations between different cameras or the camera and a colour meter will be greater than this error anyway. No two cameras will ever be truly identical and differences between lenses will cause add to this normal variation.
At the end of the day, these tiny differences are not something to worry or be concerned about. But if you do want to return the last digits back to zero you can do this by dialling the white balance all the way down to 2000K.